This invention relates to polycarbonate compositions, and more particularly, to polycarbonate compositions having improved properties such as, for example flame-retardancy.
Polycarbonates derived from reactions of organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. Polycarbonates are thermoplastic polymers which are particularly suited for the manufacture of molded products where impact strength, rigidity, toughness, thermo and dimensional stability as well as excellent electrical properties are required. The chemistry, synthesis, properties and applications of polycarbonates are discussed in Chemistry and Physics of Polycarbonates by Schnell, Interscience, 1964, and Polycarbonates by Christopher and Fox, Reinhold Publishing, 1962.
Although used extensively in commercial applications, polycarbonates generally are difficult to fabricate from melts, and polycarbonate products exhibit undesirable flammability characteristics if not treated with the proper additives.
Polycarbonates are difficult to fabricate from melts because the melts generally have exceptionally high viscosities. Attempts have been made to overcome this difficulty by the incorporation of materials known to reduce the viscosity of other resins. Some standard viscosity control agents appear to have little or no effect on the viscosity of polycarbonates. Other compounds known to lower the viscosity of other resins cause degradation of the polycarbonate resins, while still other compounds, conventionally employed to improve the workability of polymers, produce an embrittling effect on polycarbonates when they are mixed with the carbonate and the resin is subjected to elevated temperatures as in molding. Other materials, while satisfactory modifying agents for other plastics, are too volatile to be incorporated in polycarbonates which have much higher melting points than many other thermoplastics.
In order to improve the flammability resistance of polycarbonates, various approaches have been pursued including the incorporation of various additives which have been reported to improve the flame-retardant characteristics of polycarbonates treated therewith. Many patents have issued suggesting useful flame-retardant additives for polycarbonates, including, for example, U.S. Pat. Nos. 3,940,366; 3,948,851; 3,978,024; 3,953,396; 3,909,490; 3,919,167; 3,926,908; 3,931,100; 3,951,910; 4,028,297; and 4,231,920. A large number of such prior art patents are discussed in U.S. Pat. No. 4,231,920, particularly those prior art suggestions involving the use of organic alkali metal and organic alkaline earth metal salts or mixture thereof. Among the metal salts which have been suggested as being useful as flame-retardant additives for polycarbonates are the monomeric and polymeric aromatic sulfonic acids; heterocyclic sulfonic acids, monomeric or polymeric aromatic ether sulfonic acids, monomeric or polymeric phenol ester sulfonic acids, monomeric or polymeric aromatic amide sulfonic acids, etc.
U.S. Pat. No. 4,263,201 describes flame-retardant compositions comprising mixtures of aromatic carbonate polymer and minor amounts of an organic sulfonate or carboxylate, and halogenated compound. The sulfonates may be alkyl sulfonates having one to 18 carbon atoms in the alkyl group or aryl sulfonates containing 6 to 10 carbon atoms, both of which may contain halogen substituents. U.S. Pat. No. 4,007,155 also describes the use of metal salts of aliphatic sulfonic acids as flame-retardant additives for polycarbonates. The aliphatic group may contain electron-withdrawing substituents such as halo, nitro, terhalomethyl and cyano groups.